1. Field of the Invention
The present invention relates to an apparatus and method for driving a plasma display panel, and more particularly, to an apparatus and method for driving a plasma display panel in which the capability to represent the gray scale can be improved.
2. Description of the Background Art
A plasma display panel (hereinafter, referred to as a ‘PDP’) is adapted to display an image by using a visible ray generated from phosphors when ultraviolet rays generated by the discharge of a gas excite the phosphors. This PDP is advantageous it that it can provide the slimness, the compact size, higher definition and large screen, compared to the cathode ray tube (CRT).
FIG. 1 is a schematic plan view showing a conventional three-electrode AC surface discharge type PDP. FIG. 2 is a detailed perspective view illustrating the construction of the cell shown in FIG. 1.
Referring to FIGS. 1 and 2, the PDP includes scan electrodes Y1 to Yn and sustain electrodes Z which are formed on the bottom surface of an upper substrate 10, and address electrodes X1 to Xm formed on a lower substrate 18.
Discharge cells 1 of the PDP are formed every crossing of the scan electrodes Y1 to Yn, the sustain electrodes Z and the address electrodes X1 to Xm.
Each of the scan electrodes Y1 to Yn and the sustain electrodes Z includes a transparent electrode 12, and a metal bus electrode 11 that has a line width smaller than that of the transparent electrode 12 and is disposed at one edge side of the transparent electrode. The transparent electrode 12, which is generally made of ITO (indium tin oxide), is formed on the bottom surface of the upper substrate 10. The metal bus electrode, which is typically made of metal, is formed on the transparent electrode 12 and serves to reduce a voltage drop caused by the transparent electrode 12 having high resistance. On the bottom surface of the upper substrate 10 in which the scan electrodes Y1 to Yn and the sustain electrodes Z are disposed is laminated an upper dielectric layer 13 and a protective layer 14. The upper dielectric layer 13 is accumulated with wall charges generated during plasma discharging. The protective layer 14 is adapted to prevent damages of the electrodes Y1 to Yn, Z and the upper dielectric layer 13 due to sputtering caused during the plasma discharging, and improve efficiency of secondary electron emission. Magnesium oxide (MgO) is generally used as the protective layer 14.
The address electrodes X1 to Xm are formed in the lower substrate 18 in the direction in which they intersect the scan electrodes Y1 to Yn and the sustain electrodes Z. A lower dielectric layer 17 and barrier ribs 15 are formed on the lower substrate 18. The barrier ribs 24 are formed in a stripe or grating shape to separate the discharge cells 1, thus prohibiting electrical and optical interference among neighboring discharge cells 1. The phosphor layer 16 is excited with ultraviolet rays generated during the plasma discharging to generate a visible light of any one of red, green and blue lights.
An inert mixed gas such as He+Xe, Ne+Xe or He+Ne+Xe is injected into the discharge spaces of the discharge cells defined between the upper substrate 10 and the barrier ribs 15 and between the lower substrate 18 and the barrier ribs 15.
This PDP is driven with one frame being time-divided into a plurality of sub-fields having a different number of emission in order to implement the gray scale of an image. Each of the sub fields is divided into a reset period for uniformly generating discharging, an address period for selecting a discharge cell, and a sustain period for implementing the gray level according to the number of discharging. For example, if it is desired to display an image with 256 gray scales, a frame period (16.67 ms) corresponding to 1/60 seconds is divided into eight sub-fields SF1 to SF8. Each of the eight sub-fields SF1 to SF8 is subdivided into the reset period, the address period and the sustain period. The reset period and the address period of each of the sub-fields SF1 to SF8 are the same every sub-field, whereas the sustain period and the number of discharging increase in the ratio of 2n (where, n=0, 1, 2, 3, 4, 5, 6, 7) in each sub-field. Since the sustain period becomes different in each sub-field as such, the gray scale of an image can be implemented.
FIG. 3 is a block diagram showing an apparatus for driving a PDP in the prior art.
Referring to FIG. 3, the conventional apparatus for driving the PDP includes a gain adjustment unit 32, an error diffusion unit 33 and a sub-field mapping unit 34 all of which are connected between an inverse gamma control unit 31 and a data alignment unit 35, and an average picture level (APL) calculation unit 36 connected between the inverse gamma control unit 31 and a waveform generator 37.
The inverse gamma correction unit 31 linearly converts digital video data RGB of an input line 30 into the brightness for a gray scale value of a picture signal by using a 2.2 gamma table.
The gain adjustment unit 32 compensates for color temperature by adjusting an effective gain every data of R (red), G (green) and B (blue).
The error diffusion unit 33 finely adjusts the gray scale value by diffusing a quantization error of the digital video data RGB received from the gain adjustment unit 32 to neighboring cells.
The sub-field mapping unit 34 maps the data received from the error diffusion unit 33 to sub-field patterns which are previously stored therein on a per bit basis, and supplies the mapped data to the data alignment unit 35.
The data alignment unit 35 supplies the digital video data received from the sub-field mapping unit 34 to a data driving circuit of a panel 38. The data driving circuit is connected to address electrodes of the panel 38. It latches the data received from the data alignment unit 35 by 1 horizontal line and supplies the latched data to the address electrodes of the panel 38 in a 1 horizontal unit.
The APL calculation unit 36 calculates an APL in one screen unit for the digital video data RGB received from the inverse gamma correction unit 31, and outputs information on the number of a sustain pulse corresponding to the calculated APL.
The waveform generator 37 generates a timing control signal in response to the information on the number of the sustain pulse outputted from the APL calculation unit 36, and supplies the timing control signal to a scan driving circuit (not shown) and a sustain driving circuit (not shown). The scan driving circuit and the sustain driving circuit supplies the sustain pulse to scan electrodes and sustain electrodes of the panel 38 during a sustain period in response to the timing control signal from the waveform generator 37.
The conventional PDP has a limit to the capability to represent the gray scale because the gray scales are represented using sub-fields included in one frame. If the gray scales are represented using only the sub-fields, however, pseudo noise is generated in the panel 38. Therefore, in the conventional PDP, in order to improve the capability to represent the gray scale, the error diffusion unit 33 is employed. The error diffusion unit 33 calculates quantization error data of data, differentiates the calculated error data every weight, and diffuses the differentiated error data to neighboring pixels, thus expanding the gray scale. In this error diffusion method, however, error diffusion coefficients (i.e., weight) for neighboring pixels are set to be constant. Accordingly, there is a problem in that an error diffusion pattern is generated as the error diffusion coefficients are repeated every line and every frame.